This multi-institutional and interdisciplinary grant is aimed at understanding the relationship between the molecular structure of proteoglycans (PGs) and their viscoelastic and non-Newtonian flow properties. The hypothesis underlying this study is that the elaborate molecular architecture of PGs have important functional implications in various cartilaginous tissues. The knowledge gained from this study could be used to develop an understanding of how PGs might function in situ within normal articular cartilage and how dysfunction might occur in osteoarthritic human cartilage. Our strategy is based on our ability to accurately measure and theoretically model the full spectrum of the viscoelastic and non-Newtonian flow properties of biochemically characterized PGs. PG aggregates of specific molecular architecture will be reassembled from PG monomers, link protein, and hyaluronic acid from a variety of cartilaginous tissues. Enzymatic modification of the PG structure will also be pursued using trypsin and chondroitinase ABC. Of particular interest are the influence of: 1) the length of chondroitin sulfate (CS) chains, 2) keratan sulfate/chondroitin sulfate ratios, 3) length of protein core, 4) packing density of monomers along the hyaluronic acid (HA) chain, 5) presence or absence of link protein, 6) length of HA chain, 7) percent aggregation, and 8) solvent electrolyte concentration (ionic strength, valence, and pH) on the flow properties of the PG solutions. Various cartilaginous tissues will be studied to assess the effect of natural variation of PG structure and aggregation on their flow properties: 1) bovine nasal septum or rat chondrosarcoma (little or no KS), 2) mature bovine and human articular cartilage (high KS/CS ratios), 3) bovine fetal epiphyseal cartilage (huge aggregates), 4) bovine nucleus pulposus (small monomers with high KS/CS) will be measured. The rheological properties to be measured are: 1) linear viscoelastic storage modulus and loss modulus, 2) nonlinear shear rate dependent viscosity and normal stress effects, 3) thixotropic and rheopetic effects, 4) kinetic network relaxation effects, and 5) stress-overshoot effects. Theoretical modeling includes the use of nonlinear differential or integral viscoelastic laws as well as statistical-network constitutive laws to describe the full range of flow behaviors. The latter theories will be used to extract information about the density and strength of inter- and intra-molecular (PG-PG) interactions in solution.